CN112105816A

CN112105816A - Pitch bearing for wind turbine

Info

Publication number: CN112105816A
Application number: CN201880093105.2A
Authority: CN
Inventors: A·D·米纳德奥; M·J·卡马奇克; B·卡基亚
Original assignee: General Electric Co
Current assignee: General Electric Renovables Espana SL
Priority date: 2018-05-03
Filing date: 2018-05-03
Publication date: 2020-12-18
Also published as: BR112020021961A2; CA3097996A1; EP3788260A4; WO2019212557A1; EP3788260A1

Abstract

The present disclosure relates to a bearing for a wind turbine. The bearing includes an outer race, an inner race, and a radially split central race configured between the inner and outer races. Further, the center race includes a first race portion and a separate second race portion. In addition, the first race portion and the second race portion are arranged together in the axial direction. The bearing also includes a first set of rolling elements positioned between the inner and center races and a second set of rolling elements positioned between the center and outer races.

Description

Pitch bearing for wind turbine

Technical Field

The present subject matter relates generally to wind turbines, and more particularly to pitch bearings for wind turbines.

Background

Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. Modern wind turbines typically include a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transfer the kinetic energy through rotational energy to turn a shaft that couples the rotor blades to a gearbox, or directly to a generator without the use of a gearbox. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

In order to properly orient the nacelle and the rotor blades with respect to the direction of the wind, wind turbines typically include one or more yaw and/or pitch bearings. Such bearings are typically slew bearings, which are rotating ball bearings that support heavy but slowly rotating or slowly oscillating loads. A typical yaw and/or pitch bearing includes an outer race and an inner race with a plurality of ball bearings configured between the races. As such, the yaw bearing allows the nacelle to rotate and is mounted between the tower and the nacelle, while the pitch bearing allows the rotor blades to rotate and is mounted between the rotatable hub and one of the rotor blades.

As wind turbines continue to increase in size, slew bearings must similarly increase in size due to increased loading from longer rotor blades. Longer rotor blades are also accompanied by increased loads acting on the pitch bearing. Since pitch bearings are typically very expensive and may be difficult to access and replace, failure of the pitch bearing may result in a lengthy and expensive repair process.

Accordingly, an improved bearing that addresses the aforementioned problems would be welcomed in the technology.

Disclosure of Invention

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In one aspect, the present disclosure is directed to a bearing for a wind turbine. The bearing includes an outer race, an inner race, and a radially split central race configured between the inner and outer races. Further, the center race includes a first race portion and a separate second race portion. In addition, the first race portion and the second race portion are arranged together in the axial direction. The bearing also includes a first set of rolling elements positioned between the inner and center races and a second set of rolling elements positioned between the center and outer races.

In one embodiment, either or both of the first and second sets of rolling elements may comprise a plurality of rows. For example, in certain embodiments, the pitch bearing may comprise a first row of rolling elements and a second row of rolling elements aligned in the axial direction. In such embodiments, each of the first and second rows of rolling elements of the first and second sets may contact at least one of the inner race, outer race, or center race at only two contact locations.

For example, in one embodiment, the two contact locations for the first and second rows of the first set of rolling elements may include a first location on the inner race and a second location on the center race. More specifically, in such an embodiment, in a cross-sectional view of the bearing, a first line connecting two contact locations of a first row of the first set of rolling elements and a second line connecting two contact locations for a second row of the first set of rolling elements intersect to form a first angle. In certain embodiments, the first angle may range from greater than 0 degrees to about 90 degrees. In further embodiments, the first angle may be greater than 90 degrees.

Similarly, the two contact locations for the first and second rows of the second set of rolling elements may comprise a first location on the center race and a second location on the outer race. Thus, in a cross-sectional view of the bearing, a first line connecting two contact locations of a first row of the second set of rolling elements and a second line connecting two contact locations for a second row of the second set of rolling elements intersect to form a second angle. In certain embodiments, the second angle may range from greater than 0 degrees to about 90 degrees. In further embodiments, the second angle may be greater than 90 degrees.

In additional embodiments, the bearing may be used as a pitch bearing or yaw bearing for a wind turbine. In further embodiments, the first set of rolling elements and the second set of rolling elements may be ball bearings.

In another aspect, the present disclosure relates to a pitch bearing for a wind turbine. The pitch bearing includes an outer race, an inner race, and a radially split central race configured between the inner and outer races. In addition, the pitch bearing includes a first set of two-point contact rolling elements positioned between the inner and center races and a second set of two-point contact rolling elements positioned between the center and outer races. It will be appreciated that the pitch bearing may further comprise any one or a combination of the features and/or embodiments as described herein.

In yet another aspect, the present disclosure is directed to a rotor assembly for a wind turbine. The rotor assembly includes a rotor having at least one rotor blade connected to a rotatable hub by a pitch bearing. The pitch bearing includes an outer race, an inner race, and a radially split central race configured between the inner and outer races. Further, the center race includes a first race portion and a separate second race portion. In addition, the first race portion and the second race portion are arranged together in the axial direction. The bearing also includes a first set of rolling elements positioned between the inner and center races and a second set of rolling elements positioned between the center and outer races. It should be understood that the rotor assembly may further include any one or combination of the features and/or embodiments as described herein.

These and other features, aspects, and advantages of the present invention will be further supported and described with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.

Drawings

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 illustrates a perspective view of an embodiment of a wind turbine;

FIG. 2 illustrates a perspective interior view of a nacelle of the wind turbine shown in FIG. 1;

FIG. 3 illustrates a perspective view of one of the rotor blades of the wind turbine shown in FIG. 1;

FIG. 4 illustrates an isometric view of a three ring pitch bearing according to the present disclosure;

FIG. 5 illustrates a detailed cross-sectional view of one embodiment of a three ring pitch bearing connected between a hub and a rotor blade, particularly illustrating inner and outer races configured to rotate relative to a center race, according to the present disclosure;

FIG. 6 illustrates a detailed cross-sectional view of another embodiment of a three ring pitch bearing connected between a hub and a rotor blade according to the present disclosure, particularly illustrating a center race configured to rotate relative to an inner race and an outer race;

FIG. 7 illustrates a detailed cross-sectional view of yet another embodiment of a three ring pitch bearing connected between a hub and a rotor blade according to the present disclosure; and

FIG. 8 illustrates a cross-sectional view of one embodiment of a three ring pitch bearing according to the present disclosure.

Detailed Description

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. The various examples are provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.

In general, the present subject matter relates to a three ring pitch bearing for a wind turbine having an outer race, an inner race, and a radially split central race configured between the inner and outer races. Further, the center race includes a first race portion and a separate second race portion. In addition, the first race portion and the second race portion are arranged together in the axial direction. The bearing also includes a first set of rolling elements positioned between the inner and center races and a second set of rolling elements positioned between the center and outer races. Further, the split center race allows the rolling elements to achieve two-point contact of the rolling elements as described herein.

As such, the pitch bearing of the present disclosure provides many advantages not found in the cited art. For example, the pitch bearing of the present disclosure can handle increased loads due to larger rotor blades without requiring larger ball bearings or more expensive roller bearings. In addition, the pitch bearing includes a two-point contact ball bearing rather than a four-point contact ball bearing, which requires more complex machining and/or tolerances between the races. In addition, four-point contact ball bearings inherently limit the bearing geometry, which means that the bearing size and cost are increased in order to support higher loads. For example, to machine all four points of contact, the raceway of the bearing may not encircle more than half of a single ball bearing, whereas for a two-point contact ball bearing, the raceway may encircle a much larger portion of the ball bearing.

The invention is described herein as it may relate to a wind turbine bearing comprising at least a yaw bearing, a pitch bearing and/or the like. However, it should be appreciated that the unique bearing according to the principles of the present invention is not limited to use with wind turbines, but may be adapted for any suitable bearing application.

Referring now to the drawings, FIG. 1 illustrates a perspective view of an embodiment of a wind turbine 10. As shown, the wind turbine 10 generally includes a tower 12, a nacelle 14 mounted on the tower 12, and a rotor 16 coupled to the nacelle 14. Rotor 16 includes a rotatable hub 18, and at least one rotor blade 20 coupled to hub 18 and extending outwardly from hub 18. For example, in the illustrated embodiment, the rotor 16 includes three rotor blades 20. However, in alternative embodiments, rotor 16 may include more or less than three rotor blades 20. Each rotor blade 20 may be spaced about hub 18 to facilitate rotating rotor 16 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For example, the hub 18 may be rotatably coupled to a generator 224 (FIG. 2) positioned within the nacelle 14 to allow for the production of electrical energy.

Referring now to FIG. 2, a simplified interior view of an embodiment of the nacelle 14 of the wind turbine 10 shown in FIG. 1 is illustrated. As shown, the generator 48 may be disposed within the nacelle 16. Generally, generator 48 may be coupled to rotor 16 of wind turbine 10 for generating electrical power from the rotational energy generated by rotor 16. For example, rotor 16 may include a rotor shaft 50, rotor shaft 50 being coupled to hub 18 for rotation with hub 18. Generator 48 may then be coupled to rotor shaft 50 such that rotation of rotor shaft 50 drives generator 48. For example, in the illustrated embodiment, the generator 48 includes a generator shaft 52 that is rotatably coupled to the rotor shaft 50 through a gearbox 54. However, in other embodiments, it should be appreciated that the generator shaft 52 may be rotatably coupled directly to the rotor shaft 50. Alternatively, generator 48 may be directly rotatably coupled to rotor shaft 50 (commonly referred to as a "direct-drive wind turbine").

Additionally, the wind turbine 10 may include one or more yaw drive mechanisms 56 mounted to and/or through a bedplate 58, the bedplate 58 being positioned atop the wind turbine tower 12. Specifically, each yaw drive mechanism 56 may be mounted to and/or through bedplate 58 to engage a yaw bearing 60 coupled between bedplate 58 and tower 12 of wind turbine 10. Yaw bearing 60 may be mounted to bedplate 58 such that as yaw bearing 60 rotates about a yaw axis 62 of wind turbine 10, bedplate 58, and thus nacelle 14, likewise rotates about the yaw axis.

In general, it should be appreciated that yaw drive mechanism 56 may have any suitable configuration and may include any suitable components known in the art that allow such mechanism 56 to function as described herein. For example, as shown in FIG. 2, each yaw drive mechanism 56 may include a yaw motor 64 mounted to a bedplate 234. Yaw motor 64 may be coupled to a yaw gear 66 (e.g., a pinion), yaw gear 66 being configured to engage yaw bearing 60. For example, the yaw motor 64 may be coupled directly to the yaw pinion 66 (e.g., by an output shaft (not shown) extending through the bedplate 58), or indirectly to the yaw pinion 66 through a suitable gear assembly coupled between the yaw motor 64 and the yaw pinion 66. As such, torque generated by yaw motor 64 may be transferred through yaw pinion 66 and applied to yaw bearing 60 to allow nacelle 14 to rotate about yaw axis 62 of wind turbine 10. It should be appreciated that, although the illustrated wind turbine 10 is shown as including two yaw drive mechanisms 56, the wind turbine 10 may generally include any suitable number of yaw drive mechanisms 56. Similarly, it should be appreciated that yaw bearing 60 may generally have any suitable configuration, including one or more of the bearing configurations described below.

Still referring to FIG. 2, wind turbine 10 may also include a plurality of pitch bearings 68, wherein each pitch bearing 68 is coupled between hub 18 and one of rotor blades 20. As will be described below, pitch bearing 68 may be configured to allow each rotor blade 20 to rotate about its pitch axis 70 (e.g., via a pitch adjustment mechanism), thereby allowing the orientation of each blade 20 to be adjusted relative to the direction of the wind. It should be appreciated that, as used herein, the term "slew bearing" may be used to refer to one of yaw bearing 60 of wind turbine 10 and/or pitch bearing 68 of wind turbine 10 or any other similar bearing.

Referring now to FIG. 3, a perspective view of one of the rotor blades 20 illustrated in FIGS. 1 and 2 is illustrated, in accordance with aspects of the present subject matter. As shown, the rotor blade 20 includes a blade root 22 configured for mounting the rotor blade 20 to the hub 18 (FIG. 1) of the wind turbine 10 and a blade tip 24 disposed opposite the blade root 22. The body 26 of the rotor blade 20 may extend longitudinally between the blade root 22 and the blade tip 24, and may generally serve as a shell for the rotor blade 20. As generally understood, the body 26 may define an aerodynamic profile (e.g., by defining an airfoil-shaped cross-section, such as a symmetrical or cambered airfoil-shaped cross-section) to enable the rotor blade 20 to capture kinetic energy from wind using known aerodynamic principles. Thus, the body 26 may generally include a pressure side 28 and a suction side 30 extending between a leading edge 32 and a trailing edge 34. In addition, the rotor blade 20 may have a span 36 defining the overall length of the body 26 between the blade root 22 and the blade tip 24, and a chord 38 defining the overall length of the body 26 between the leading edge 32 and the trailing edge 34. As generally understood, the chord 38 may vary in length relative to the span 26 as the body 26 extends from the blade root 22 to the blade tip 24.

Furthermore, as shown, the rotor blade 20 may also include a plurality of T-bolts or root attachment assemblies 40 for coupling the blade root 20 to the hub 18 of the wind turbine 10. In general, each root attachment assembly 40 may include a barrel nut 42 and a root bolt 44, the barrel nut 42 being mounted within a portion of the blade root 22, the root bolt 44 being coupled to the barrel nut 42 and extending from the barrel nut 42 so as to project outwardly from a root end 46 of the blade root 22. By projecting outwardly from root end 46, root bolt 44 may generally serve to couple blade root 22 to hub 18 (e.g., via one of pitch bearings 50), as will be described in more detail below.

Referring now to fig. 4-8, various views of pitch bearing 68 are illustrated, according to aspects of the present disclosure. As generally shown, pitch bearing 68 includes an outer race 74, an inner race 76, a radially split central race 78 configured between inner and

outer races

76, 74, and a plurality of rolling

elements

84, 86 disposed between

races

74, 76, 78. For example, in one embodiment, the rolling

elements

84, 86 may be ball bearings. More specifically, as shown, the center race 78 has a radially split configuration (i.e., split in a radial direction as indicated by arrow 35) with a first race portion 80 and a split second race portion 82 aligned in the axial direction 37. More specifically, as shown, the center race 78 is split horizontally along a split line 91. Further, the first portion 80 and the second portion 82 may be symmetrical or asymmetrical. Additionally, as shown in fig. 6, the center race 78 is rotatable relative to the inner and

outer races

76, 74 via rolling

elements

84, 86. Alternatively, as shown in fig. 5, inner race 76 and outer race 74 may be rotatable relative to central race 78. More specifically, as shown, pitch bearing 68 includes a first set of rolling elements 84 positioned between inner race 76 and first race portion 80 of center race 78 and a second set of rolling elements 86 positioned between second race portion 82 of center race 78 and outer race 74. For example, as shown in fig. 8, the rolling

elements

84, 86 may be positioned within one or

more raceways

79, 81, 83 of the

races

74, 76, 78.

Further, as shown in fig. 5, the outer race 74 and the inner race 76 may generally be configured to be mounted to a hub flange 75 of the hub 18 using a plurality of hub bolts 77 and/or other suitable fastening mechanisms. Similarly, the center race 78 may be configured to be mounted to the blade root 22 using the root bolts 44 of the root attachment assembly 40. For example, as shown in fig. 5, each root bolt 44 may extend between a first end 45 and a second end 47. As such, the first end 45 may be configured to be coupled to a portion of the central race 78 (such as by coupling the first end 45 to the central race 78 using an attachment nut and/or other suitable fastening mechanism). Second end 47 of each root bolt 44 may be configured to be coupled to blade root 22 via barrel nut 42 of each root attachment assembly 40. Thus, center race 78 may be configured to rotate relative to outer race 74 and inner race 76 (via rolling

elements

84, 86, rolling

elements

84, 86 via a pitch adjustment mechanism engaging teeth 71) to allow adjustment of the pitch angle of each rotor blade 20.

In an alternative embodiment, as shown in fig. 6, outer race 74 and inner race 76 may be configured to rotate relative to central race 78. In such embodiments, the center race 78 may include a plurality of teeth 73, the teeth 73 configured to engage a pitch adjustment mechanism, as discussed below.

As shown in fig. 5, such relative rotation of the outer race 74 and the inner race 76 may be achieved using, for example, a pitch adjustment mechanism (not shown) mounted within a portion of the hub 18. In general, the pitch adjustment mechanism may include any suitable components and may have any suitable configuration that allows the mechanism to function as described herein. For example, in certain embodiments, the pitch adjustment mechanism may include a pitch drive motor (e.g., an electric motor), a pitch drive gearbox, and a pitch drive pinion. In such embodiments, the pitch drive motor may be coupled to the pitch drive gearbox such that the motor imparts mechanical force to the pitch drive gearbox. Similarly, a pitch drive gearbox may be coupled to the pitch drive pinion for rotation with the pitch drive pinion. The pinion may, in turn, be in rotational engagement with one of the

races

74, 76, 78. For example, a plurality of gear teeth (e.g., teeth 71, 73) may be formed along an inner circumference of one of the

races

74, 76, 78 (i.e., to the central race 78 or inner and outer races 76, 74), with the

gear teeth

71, 73 configured to mesh with corresponding gear teeth formed on the pinion gear. Thus, due to the meshing of the gear teeth, rotation of the pitch drive pinion causes rotation of the center race 78 relative to the outer race 74 and the inner race 76, and thus rotation of the rotor blade 20 relative to the hub 18. Additionally, the

races

74, 76, 78 may rotate relative to one another using any other suitable means, including, for example, hydraulics.

Additionally, either or both of the first and second sets of rolling

elements

84, 86 may include multiple rows, for example, first and

second rows

85, 87, 88, 89 of rolling elements aligned along the axial direction 37. In such an embodiment, each of the first and

second rows

85, 87, 88, 89 of rolling elements of the first and

second sets

84, 86 contacts at least one of the inner race 76, outer race 74, and/or center race 78 at only two contact locations.

More specifically, as shown in the illustrated embodiment, the two contact locations for the first and

second rows

85, 88 of the first set of rolling elements 84 may include a first location 90 on the inner race 76 and a second location 92 on the first race portion 80 of the center race 78. Thus, as shown, in the cross-sectional views of the pitch bearing 68 as shown in fig. 5-7, a first line 93 connecting the two

contact locations

90, 92 of the first row 85 of the first set of rolling elements 84 and a second line 94 connecting the two

contact locations

90, 92 of the second row 88 for the first set of rolling elements 84 may intersect to form a first angle, which may be optimized for the respective bearing. In certain embodiments, the first angle may be in a range from about 0 degrees to about 90 degrees. For example, as shown, the first angle is about 90 degrees. In additional embodiments, the first angle may be greater than 90 degrees.

Similarly, the two

contact locations

95, 96 for the first and

second rows

87, 89 of the second set of rolling elements 86 may include a first location 95 on the second race portion 82 of the center race 78 and a second location 96 on the outer race 74. Thus, in the cross-sectional views of the pitch bearing 68 as shown in fig. 5-7, a first line 97 connecting the two

contact locations

95, 96 of the first row 87 of the second set of rolling elements 86 and a second line 98 connecting the two

contact locations

95, 96 for the second row 89 of the first set of rolling elements 86 intersect to form a second angle. In certain embodiments, the second angle may be in a range from about 0 degrees to about 90 degrees. For example, as shown, the second angle is about 90 degrees. As such, for the illustrated embodiment, the two contact locations for each of the rolling elements are spaced approximately 180 degrees apart. In additional embodiments, the second angle may be greater than 90 degrees. It should also be understood that the first and second angles may be equal or different.

In further embodiments, the closer the first and second contact angles are to the axial direction 37, the more resistant the bearing 68 may be to fatigue loading cycles (i.e., caused by multiple loading cycles). Alternatively, the closer the first and second contact angles are to the radial direction 35, the more the bearing 68 may be able to resist extreme loads. Thus, the bearing 68 of the present disclosure allows all raceway contact angles to be optimized and separated by an angle.

Referring particularly to fig. 8, a cross-sectional view of the bearing 68 is illustrated to further illustrate assembly of the bearing 68. More specifically, as shown, the second race portion 82 of the center race 78 may be lowered onto the surface. Portions of the rolling

elements

84, 86 may then be placed within the lower portion of the raceway 79 of the center race 78. As such, the inner race 76 and the outer race 74 may then be lowered about the center race 78 containing the lower row of rolling

elements

84, 86 such that the lower row of rolling

elements

84, 86 fit within the

raceways

81, 83 of the inner race 76 and the outer race 74, respectively. The top row of rolling

elements

84, 86 may then be placed in the upper raceway between the inner and

outer races

76, 74 and the center race 78. The first race portion 80 of the center race 78 may then be secured atop the second race portion 82 of the center race 78.

Additionally, any suitable number of

rolling elements

84, 86 may be employed. Further, the rolling

elements

84, 86 may be arranged in any suitable configuration. For example, as mentioned, two rows of rolling

elements

84, 86 may be employed, with each of the rolling

elements

84, 86 being circumferentially spaced between the outer race 62 and the inner race 64. In another embodiment, a single row or multiple axially spaced rows of rolling

elements

84, 86 may be utilized in pitch bearing 68 to provide additional strength. For example, in various embodiments, three or more rows of rolling

elements

84, 86 may be employed.

Additionally, in several embodiments, a plurality of lubrication ports 65 may be defined through the

races

74, 76, 78. In general, each lubrication port 65 may be configured to supply a suitable lubricant (e.g., grease, etc.) from a location external to pitch bearing 68 to a location between

races

74, 76, 78. Additionally, to maintain lubricant within pitch bearing 68, any gaps defined between

races

74, 76, 78 may be sealed using a suitable sealing mechanism. For example, as shown in fig. 5-7, pitch bearing 68 includes a plurality of sealing mechanisms 67 configured between

races

74, 76, 78 to maintain lubricant within bearing 68.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A bearing for a wind turbine, comprising:

an outer race;

an inner race;

a radially split central race configured between the inner and outer races, the central race including a first race portion and a separate second race portion, the first and second race portions arranged together in an axial direction;

a first set of rolling elements positioned between the inner race and the center race; and

a second set of rolling elements positioned between the outer race and the center race.

2. Bearing according to claim 1, wherein at least one of the first set of rolling elements or the second set of rolling elements comprises at least a first row of rolling elements and a second row of rolling elements.

3. The bearing of claim 2, wherein each of the first and second rows of rolling elements of the first and second sets contacts at least one of the inner race, the outer race, or the center race at only two contact locations.

4. The bearing of claim 3, wherein the two contact locations for the first and second rows of the first set of rolling elements comprise a first location on the inner race and a second location on the center race.

5. The bearing of claim 4, wherein in a cross-sectional view of the bearing, a first line connecting the two contact locations of the first row of the first set of rolling elements and a second line connecting the two contact locations for the second row of the first set of rolling elements intersect to form a first angle, the first angle being in a range from greater than 0 degrees to about 90 degrees.

6. The bearing of claim 3 wherein the two contact locations for the first and second rows of the second set of rolling elements comprise a first location on the center race and a second location on the outer race.

7. The bearing of claim 6, wherein in a cross-sectional view of the bearing, a first line connecting the two contact locations of the first row of the second set of rolling elements and a second line connecting the two contact locations for the second row of the second set of rolling elements intersect to form a second angle, the second angle being in a range from greater than 0 degrees to about 90 degrees.

8. The bearing of claim 1, wherein the bearing comprises at least one of a pitch bearing or a yaw bearing of the wind turbine.

9. The bearing of claim 1, wherein the first set of rolling elements and the second set of rolling elements comprise ball bearings.

10. A pitch bearing for a wind turbine, comprising:

an outer race;

an inner race;

a radially split center race configured between the inner and outer races;

a first set of two-point contact rolling elements positioned between the inner race and the center race; and

a second set of two-point contact rolling elements positioned between the center and outer races.

11. A rotor assembly for a wind turbine, comprising:

a rotor comprising at least one rotor blade connected to a rotatable hub by a pitch bearing, the pitch bearing comprising:

an outer race;

an inner race;

a radially split central race configured between the inner and outer races, the central race including a first race portion and a separate second race portion;

a second set of rolling elements positioned between the center race and the outer race.

12. The rotor assembly of claim 11 wherein at least one of the first set of rolling elements or the second set of rolling elements comprises at least a first row of rolling elements and a second row of rolling elements.

13. The rotor assembly of claim 12 wherein each of the first and second rows of rolling elements of the first and second sets contacts at least one of the inner race, the outer race, or the center race at only two contact locations.

14. The rotor assembly of claim 13 wherein the two contact locations for the first and second rows of the first set of rolling elements comprise a first location on the inner race and a second location on the center race.

15. The rotor assembly of claim 14 wherein, in a cross-sectional view of the bearing, a first line connecting the two contact locations of the first row of the first set of rolling elements and a second line connecting the two contact locations for the second row of the first set of rolling elements intersect to form a first angle, the first angle being in a range from greater than 0 degrees to about 90 degrees.

16. The rotor assembly of claim 13 wherein the two contact locations for the first and second rows of the second set of rolling elements comprise a first location on the central race and a second location on the outer race.

17. The rotor assembly of claim 16 wherein, in a cross-sectional view of the bearing, a first line connecting the two contact locations of the first row of the second set of rolling elements and a second line connecting the two contact locations for the second row of the second set of rolling elements intersect to form a second angle, the second angle being in a range from greater than 0 degrees to about 90 degrees.

18. The rotor assembly of claim 11, wherein the center race is secured to the rotor blade, and the inner and outer races are secured to the rotatable hub.

19. The rotor assembly of claim 11 wherein the central race is secured to the rotatable hub and the inner and outer races are secured to the rotor blades.

20. The rotor assembly of claim 11, wherein the bearing comprises at least one of a pitch bearing or a yaw bearing of the wind turbine.